A Gantt chart that is a schedule
Bars computed from dependencies and your working week, not dragged into place. Change a duration and everything downstream moves — because the picture is the plan.
A Gantt chart that is a schedule, not a drawing
Bars are computed from dependencies and a working calendar. Change a duration and everything downstream moves, because the picture is the plan rather than a picture of one.
Activities
Predecessors accept A, A:SS+2, B:FF-1. A duration of 0 is a milestone.
The same schedule as a table
Every chart here has one. A bar chart is not readable by a screen reader and not printable at a useful size.
How the bars are placed
Positions come from a full CPM pass: forward pass for earliest dates, backward pass for latest, float as the difference. Bars are not positioned by hand and cannot be dragged out of agreement with the dependencies.
Durations are working days. The bar is drawn across calendar days, so a bar spanning a weekend looks longer than its duration — that gap is the weekend, and shading it is why the option exists.
A finish date is the last day worked, not the day after. Internally a finish is the instant work stops; the distinction is the source of most off-by-one errors in scheduling and is handled once, consistently.
Most Gantt charts are drawings
A bar dragged to a new position in a drawing tool tells you where somebody wished the work would happen. Nothing downstream moves, no dependency is checked, and the chart quietly stops describing the plan the moment the first date changes.
Here the bars are output. Change a duration and everything that depends on it moves, because the arrangement was computed from the dependencies rather than arranged by hand. If that produces an unpleasant picture, the picture is correct and the plan is the problem.
The gaps in a bar are weekends
Durations are working days and the chart is drawn on calendar days, so a five-day task starting on a Thursday spans nine days on the page. That is not an error — it is the weekend, and it is exactly the thing people forget when reading a date off a chart.
Shading the non-working days makes it visible. Turn the shading off and the same chart becomes quietly misleading, which is a reasonable argument for leaving it on.
Float is the part worth looking at
The bar shows when work is planned. The grey tail after it shows how far it could slip before the project is affected. Activities with no tail are the ones where a single bad day costs a day of the finish date.
A chart where almost nothing has a tail is not a tight plan so much as an over-constrained one, and it usually means dependencies have been drawn more rigidly than the work actually requires.
There is always a table
A bar chart cannot be read by a screen reader, does not survive being printed small, and hides exact dates behind pixel positions. The table below the chart carries the same numbers and is the version to send to anyone who has to act on a specific date.